The origin of crude oil
5 marks · HardCrude oil formed over millions of years from the remains of organisms.
Describe what happened to the dead sea plants and animals that led to the formation of crude oil.
State two conditions necessary for crude oil to form from these remains.
Explain why crude oil is considered a non-renewable resource.
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(a) The soft parts of plants and animals were buried by layers of sediment, and over millions of years, heat and high pressure changed them into crude oil.
(b) Two conditions: (1) high pressure; (2) high temperature/heat; (allow absence of oxygen, burial by sediment).
(c) Crude oil cannot be replaced in a human lifetime/it takes millions of years to form.
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Marking points
B1 (a) · 1 mark · Mentions burial of dead organisms under sediment/sea floor.
B2 (a) · 1 mark · Mentions transformation to crude oil by heat and pressure over millions of years.
B3 (b) · 1 mark · States one relevant condition (e.g., high pressure, high temperature, absence of oxygen, sediment coverage).
B4 (b) · 1 mark · States a second relevant condition (from list above), not a repeat.
B5 (c) · 1 mark · Explains crude oil is non-renewable because it cannot be replaced quickly/it takes millions of years to form.
Worked solution
a) After sea plants and animals died, their remains settled at the bottom of the sea and were buried by layers of sediment. The soft parts were gradually changed into crude oil by heat and high pressure over millions of years.
b) Two required conditions: (1) High pressure. (2) High temperature (heat). (Accept lack of oxygen or burial by sediment).
c) Crude oil is non-renewable because it takes millions of years to form and cannot be replaced within a human lifetime.